The present disclosure relates to a process for reducing haze in a heavy base oil and a hydroisomerization catalyst system having reduced haze and, more particularly, to a process for effectively reducing haze while significantly minimizing yield loss in a hydroisomerization process, and a hydroisomerization catalyst system applicable to the same.
Catalytic dewaxing processes change undesired molecules in raw materials to molecules having desired characteristics for specific purposes. More specifically, the catalytic dewaxing processes may be applicable in various fields through being used to improve the characteristics of base oil that forms lubricating oil, as well as to enhance the cold flow properties of diesel oil. Such catalytic dewaxing processes are performed by cracking or isomerizing molecules in raw materials. Since dewaxing methods, among the variety of dewaxing methods, which depend mainly on cracking, produce large amounts of products having a low viscosity index, the cracking dominant dewaxing methods have a low yield compared to dewaxing methods largely relying on isomerization. Thus, the isomerization dominant dewaxing methods have been preferred, in which hydroisomerization catalysts are used.
Meanwhile, in refining processes such as the production of lubricating oil and diesel oil, the importance of hydroisomerization reactions in converting long-chain, normal paraffins (n-paraffins) to iso-paraffins has emerged. This is the reason that the long-chain, n-paraffins have low-temperature fluidity, and thus cannot meet the recently required standards of fuel oil and lubricating oil products. In particular, the quality of crude oil as a raw material has deteriorated in recent years. However, with the development of automobile engine technology, higher quality products are required for fuel oil and lubricating oil products. For example, hydroisomerization reactions may be applied to processes for manufacturing high-octane gasoline using C4-C7 hydrocarbon as a raw material, to processes for manufacturing high-quality, high-cetane diesel oil having improved cold flow properties using C7-C15 hydrocarbon as a raw material, and to processes for manufacturing high-quality lubricating oil having a high viscosity index and improved cold flow properties using C15 or higher hydrocarbon as a raw material.
The above-mentioned hydroisomerization reactions have been performed mainly by bi-functional catalysts, and the catalysts typically consist of metal components having a hydrogenation/dehydrogenation function and of supports having acid sites for a skeletal isomerization reaction. In this regard, various materials, such as amorphous silica-alumina, clay, and zeolite, which is crystalline silica-alumina, have been known as supports having acid sites. In particular, zeolites are not only maintained to have a stable structure, even under severe reaction conditions, but also have a wide surface area and a plurality of acid sites, thereby being suitable for an isomerization reaction.
Research has been conducted into zeolites having excellent shape selectivity, whereby an undesired decomposition reaction of hydrocarbons to be processed is preferably suppressed, while maximizing an isomerization reaction of the hydrocarbons. It has been reported that ZSM-22, ZSM-23, EU-2 and ZSM-48 zeolites having a 1-dimensional 10-ring pore structure have excellent shape selectivity in a hydroisomerization reaction.
Meanwhile, according to the catalogues of the International Zeolite Association (IZA), EU-2, ZSM-48, ZBM-30 and EU-11 zeolites belong to the ZSM-48 family, which have a similar X-ray diffraction (XRD) pattern, i.e. a crystal structure. As described above, U.S. Pat. No. 6,984,309 discloses a technology that improves the viscosity index, low-temperature fluidity, and the like, of hydrocarbon oil by using EU-2 zeolite or EU-2 zeolite and a binder as a support, and performs a hydroisomerization reaction in the presence of a catalyst in which a hydrogenation/dehydrogenation metal is loaded on the support.
In heavy base oil or bright stock having a relatively high boiling point, compared to common base oil, it has been found to be difficult to meet cold flow properties by a conventional dewaxing method that has been applied to the base oil. Furthermore, even when the conventional dewaxing method satisfies the standards of low-temperature fluidity, it is very difficult to remove haze-inducing substances. Therefore, reducing haze from heavy base oil or bright stock has not been found to be easy. Paraffins, such as, commonly, long-chain n-paraffins, partially isomerized long-chain n-paraffins, and cycloparaffins, have been known as haze-inducing substances. Such haze-inducing substances do not cause any problem at room temperature. However, under conditions of a comparatively low temperature, such as 0° C., and a relatively long term, such as 7 days, the haze-inducing substances may agglomerate with each other, resulting in a haze that makes products cloudy. Also, haze-inducing substances may be removed under more severe dewaxing reaction conditions, such as an increase in reaction temperature, which may accompany undesired yield loss.
Therefore, a method of selectively removing haze-inducing substances, while minimizing yield loss, is required, and many attempts at the same have been reported. U.S. Pat. No. 4,919,788 discloses a method of removing haze-inducing substances by adding a catalyst consisting of a support of an ultrastable Y zeolite or a beta-type (BEA) zeolite to a catalyst consisting of a support of a common dewaxing catalyst such as ZSM-22 or ZSM-23 zeolite. Moreover, U.S. Pat. No. 6,051,129 discloses a method of removing haze-inducing substances by adding a catalyst consisting of a EU-1 zeolite support to a catalyst consisting of a support of a common dewaxing catalyst, such as ZSM-48 or ZSM-32 zeolite. However, these methods are undesirable because, although haze-inducing substances are removed, they involve a decrease in yield.
Therefore, it is expected that when a method of selectively removing haze-inducing substances while minimizing yield loss is provided in a dewaxing process for a heavy base oil containing haze-inducing substances, the method will be widely applicable in the related art.